One applicant of this application has proposed, in the Japanese Patent Application Laid Open No. 119776/1992, an image pick-up apparatus having an electronic shutter function to carry out exposure time adjustment without use of a mechanical iris by controlling the charge storage time of a solid-state image pick-up device (CCD image sensor) of the Interline Transfer (IT) type.
In this image pick-up apparatus, an approach is employed to read out, to the vertical transfer sections, charges stored in respective pixels of the photoelectric converting section of the CCD image sensor by a read-out signal shown in FIG. 1(b) outputted at the vertical blanking period VBLK during which a vertical blanking signal shown in FIG. 1(a) is caused to be low level. The charge storage time of the CCD image sensor is controlled by a reset signal shown in FIG. 1(c). When this reset signal is delivered, the CCD image sensor sweeps out charges stored in the pixels into the overflow drain.
For this reason, for a time period during which the reset signal is delivered (charge sweep-out period), no charge is stored into the CCD image sensor. Accordingly, effective charges are stored (accumulated) into the photoelectric converting section of the CCD image sensor from the time point when the reset signal delivered to the CCD image sensor is stopped. By controlling the timing at which the reset signal is stopped, it is possible to control the charge storage time, i.e., the shutter speed.
Since the image pick-up apparatus can vary the shutter speed in dependency upon movement (motion) of an object by using such an electronic shutter function, it is advantageous in taking in images particularly in high speed moving object (body).
At present, an image pick-up apparatus used, e.g., mainly for FA and adapted to carry out image pick-up of a moving object is known. This image pick-up apparatus has a configuration as shown in FIG. 2, for example. When an object 201 moving on a movement path 200 moves up to the position in front of an image pick-up section 202, a position detecting section 203 detects this movement of the object to deliver, to a shutter signal generating circuit 204, a trigger signal which falls to low level at time t11 of FIG. 3(a) (i.e., the shutter control signal is caused to be active).
When the trigger signal is delivered, the shutter signal generating circuit 204 delivers, to a CCD control circuit 205, a shutter control signal which rises to high level at the time t11 of FIG. 3(b).
For a time period during which the shutter control signal is not active, the CCD control circuit 205 delivers a reset signal (indicating the state where the shutter control signal is inactive) for sweeping out charges stored in the photoelectric converting section of the CCD image sensor 206 into the overflow drain. Thus, for a time period during which the circuit 206 is supplied with the reset signal, no charge is stored into respective pixels of the photoelectric converting section of the CCD image sensor 206. However, when the trigger signal is delivered, the circuit 205 stops the reset signal (allow the shutter control signal to be active) delivered to the CCD image sensor 206. Thus, storage (accumulation) of effective charges into respective pixels of the photoelectric converting section of the CCD image sensor 206 is started.
More particularly, the CCD control circuit 205 is supplied with a vertical synchronizing signal which represents low level for a time period from time t11 to time t12 of FIG. 3(c) and a horizontal synchronizing signal shown in FIG. 3(d) from a synchronizing signal generating circuit 207. When the shutter control signal of H level (i.e., in active state) is delivered, the CCD control circuit 205 counts, by nine (9), the number of pulses of the horizontal synchronizing signal shown in FIG. 3(d) from the time t11 at which the vertical synchronizing signal shown in FIG. 3(c) falls thereafter to count the number of pulses of a clock signal (hereinafter simply referred to as clock pulses depending upon circumstances) by several hundreds thereafter to deliver a read-out signal indicated at time t13 of FIG. 3(e) to the CCD image sensor 206.
Thus, for a time period from the time when the shutter control signal of H level (i.e., in active state) is delivered to the CCD image sensor 206 at the time t11 of FIG. 3(b) up to the time when the read-out signal is delivered to the CCD image sensor 206 at time t13 of FIG. 3(e), charges corresponding to image pick-up light irradiated through an imaging lens will be stored (accumulated) into the CCD image sensor 206. This time period from the time t11 to the time t13 is the charge storage time.
In the above-mentioned timing chart, FIG. 3(f) indicates the vertical blanking period VBLK.
Charges read out from the CCD image sensor 206 are delivered to a signal processing circuit 209 as an image pick-up signal. The signal processing circuit 209 implements a signal processing to add a synchronizing signal to the image pick-up signal, etc. to output this signal through output terminal 210 as a video signal. The video signal outputted through the output terminal 210 is delivered to, e.g., monitor. Thus, it is possible to analyze the state of the object 201 in the case where the object 201 is moved.
Since such image pick-up apparatus adapted for carrying out image pick-up of a moving object is used mainly for FA, there are instances where the object 201 shown in FIG. 2 is moved at a high speed to carry out imaging (image pick-up) operation by high speed shutter, e.g., 1/10000 sec., etc.
However, the above-mentioned image pick-up apparatus counts, e.g., by nine (9), the number of pulses of the horizontal synchronizing signal, from falling of the vertical synchronizing signal thereafter to deliver, to the CCD image sensor, a read-out signal at the timing where clock pulses are counted by several hundreds. Namely, the output timing of the read-out signal is fixedly set in advance on the basis of pixel arrangement of the CCD image sensor.
Accordingly, the charge storage time of the image pick-up apparatus could not be shortened so that it is equal to a time less than the time from the falling time of the vertical synchronizing signal up to the time when the read-out signal is outputted. For this reason, the conventional image pick-up apparatus could not carry out image pick-up operation by high speed shutter such as 1/10000 sec., etc.
The above-mentioned image pick-up apparatus is adapted to start storage (accumulation) of effective charges in accordance with a trigger signal delivered from the position detecting section 203 as described above. Namely, this image pick-up apparatus operates in accordance with the timing of the trigger signal delivered from the position detecting section 203.
Meanwhile, there are instances where there is a need such that an image processing equipment is used to implement image processing to a video signal from the image pick-up apparatus. Generally, the image processing equipment operates with a predetermined synchronizing signal being as reference. For this reason, e.g., in the case where video signals from a plurality of image pick-up apparatuses or video recording/reproducing apparatuses, etc. are synthesized, or the like, it is necessary to deliver a video signal synchronous with a synchronizing signal serving as reference to an image processing equipment.
In more practical sense, when a trigger signal is delivered, as shown in FIG. 4(a), for example, at an arbitrary timing, this image pick-up apparatus delivers the read-out signal shown in FIG. 4(b) to the CCD image sensor after a predetermined charge storage time, i.e., exposure time to read out charges stored in respective pixels of the photoelectric converting section to the vertical transfer sections, and to generate a vertical synchronizing signal V-SYNC simultaneously therewith to output, as an image pick-up signal, through the horizontal transfer section, the charges which have been read out to the vertical transfer sections at a timing synchronized with the generated vertical synchronizing signal V-SYNC.
Namely, this image pick-up apparatus attempts to generate vertical synchronizing signals V-SYNC of a fixed period after the trigger signal is delivered, as shown in FIG. 5(c), for example, wherein when a trigger signal shown in FIG. 5(a) is delivered, a read-out signal shown in FIG. 5(b) is delivered to the CCD image sensor after a predetermined exposure time to read out, to the vertical transfer sections, charges stored in respective pixels of the photoelectric converting section, and to generate a vertical synchronizing signal V-SYNC simultaneously therewith.
In this image pick-up apparatus, however since video signals are outputted as shown in FIG. 6(b) at random time intervals in accordance with trigger signals delivered at arbitrary timings, i.e., at random as shown in FIG. 6(a), it is impossible to output the vertical synchronizing signals V-SYNC at a fixed period in practice.
Meanwhile, in video processing equipments, e.g., frame memory, monitor or the like for carrying out processing by using video signals from such an image pick-up apparatus, their operations are required to be synchronized with video signals delivered thereto.
However, in such video processing equipments, it is very difficult from a technical point of view to synchronize their operations with synchronizing signals of random period. Such a way of synchronization is not carried out in general.
An object of this invention is to provide an image pick-up apparatus capable of effecting high speed shutter operation.
Another object of this invention is to provide an image pick-up apparatus capable of controlling the timing at which a video signal obtained by imaging is outputted, and easy to take synchronization with external equipments.
A further object of this invention is to provide an imaging (image picking up) system capable of outputting video signals from an image pick-up apparatus (unit) in a manner synchronized with a synchronizing signal from an image taking-in unit.
A still further object of this invention is to provide a control unit and a control system which are adapted to output video signals from an image pick-up apparatus in a manner synchronized with a synchronizing signal from an image taking-in unit.